Abstract

Acidovorax radicis N35 is a plant growth promoting endophytic bacterium in wheat and barley. The perception by plants can be characterized using RNAseq, q-PCR and selected metabolite analyses. It could be shown, that barley seedlings are quickly responding to bacterial colonization by a reprogramming of gene expression and priming of defense responses. Especially, the role of quorum sensing auto-inducers of the N-acyl homoserine lactone (AHL) type in the perception by plants should be analyzed. A. radicis N35 produces 3-hydroxy-C10-homoserine lactone (3-OH-C10-HSL) as major AHL-compound. In this communication the influence of A. radicis N35-produced 3-OH-C10-HSL on barley seedlings was investigated by comparing wild type and an araI insertion mutant, lacking AHL-production. The comparison of inoculation effects of the A. radicis N35 wild type and the araI mutant discovered remarkable differences. While the N35 wild type colonized plant roots effectively by forming biofilm-like structures on the root surface, the araI mutant occurred at the root surface as single cells. In addition, in a mixed inoculum of wild type and araI mutant, the wild type was predominant in colonization compared to the araI mutant. Nevertheless, a significant plant growth promotion effect could be shown after inoculation of barley with the wild type and the araI mutant in soil after 2 months. A. radicis N35 wild type showed less induction of early defense responses in plant RNA-expression analysis, whereas the araI mutant caused e.g. increased expression of flavonoid biosynthesis genes, which was corroborated by the accumulation of several flavonoid compounds like saponarin and lutonarin in leaves of root inoculated barley seedlings. Thus, it can be concluded, that the synthesis of 3-OH-C10-HSL by A. radicis has implications on the colonization efficiency of plant roots and the perception by the host plant barley.